Semi ot - Drum brakes warped

[rockrat]

I have a truck that I am having problems with the drum brakes on. Here is a post that I made on another forum looking for a second set of eyes or oposing thoughts on the subject.

So the old girl ('98 F150 4X4) is giving me issues. I have used this truck a bit for towing so now that the brakes are giving me trouble I figure that I may well need to give them super extra attention.

After the last tow I noticed that the brake pedal was surging like I had a warped rotor and it was moving a bit more than I liked. So, I started to look around. Front rotors looked ok but they will need replaced soon. Although I did find a few other issues.

Replaced or fixed
1) Rusty rear brake line, main master cylinder line to rear line and the two running to the wheel cylinders
2) Rusty line from master cylinder to the front brakes. Including across the front end to passenger side.
3) All rear hardware, shoes and drums.

Now, all was good till a while back and I found that I had a pulse in the brake pedal again. Now I took the drums off and checked them. They have 0.050" to 0.075" runout! What? Warped again? So I decided the the cheap drums burned me. Bought new drums and got the mid range drums.

After 200 miles, more pedal pulsing and drums are warped about as bad as last time. I rechecked all the rear hardware, primary shoe vs secondary shoe, air in the front lines etc.

The brake pedal moves a bit better than half way to get good braking and then it seems that the rear end twists and makes noise similar to a proportional valve problem.

All I can imagine is either a bad master cylinder that is not proportioning the front/rear brakes correctly, along with a booster that is going bad (it does swish at times) or ?????

I don't mind putting a bit of money in this truck cause it has served me well but am I missing something more simple?

Your thoughts.
Thanks~

I didnt receive many replies. I think that I'm on the right track but, what do you all think? This will be a tedious job and I just want to make sure that I'm not missing something simple. Oh, 150k miles. This truck aint a young pup but she has served me well so far.

rock~

[jimmstruk]

Rock, if I understand correctly, your warped drums are on the rear and no problem with the front rotors? My thoughts are that the flex hose from the frame to the axle may have deteriorated internally, not letting the fluid go back to master cylinder, causing the brakes to stay partially applied, causing the drums to overheat and warp the drums! I have run in to several cases of hose failure where power booster will apply brakes but springs are not strong enoughto fully release them. JIM

[kendall]

did you replace the rubber line to the axle?

A common failure mode on them is for the liner to come loose and act as a valve so the brakes will remain applied for a while after they're released.

Ken.

[tom in nh]

Are you using a torque wrench to seat them lugnuts?
How much weight are you towing?
Are the drums hot after moderate driving / blue in color?
E-brake system ok? No dragging?
More clues may help.

[Ken_Shea]

Jim is absolutely on the right track, heat is what warps them and rotors. If the rubber hose is secured to the frame via a metal clamp around the hose that can be the likely culprit, everything looks fine but rust builds up between the clamp and the hose closing off fluid flow.

Jack up the back end, pump the brakes and see if they still turn freely or with very little drag.
Also things to look for are improper brake adjustment, rust on the mating flange of the axle, improper lug nut torque, although rare, a defective proportioning valve, corroded wheel cylinders.

Ken

[Willy]

Some good advice so far.
Ken's suggestion to jack up the back axle and check for brake drag would have been my first thought as well.
Have you replaced the return springs or rebuilt or replaced the rear wheel cylinders?
Like Ken mentioned corroded wheel cylinders and old return springs are definitely a factor on a ten year old vehicle. Brake fluid being hydroscopic in conjunction with cast iron wheel cylinders are a recipe for corrosion.
How many people purge old brake fluid every two years? Yeah me neither.
Another possible factor as you already mentioned is the proportioning valve directing too much pressure to the drum brake side of the circuit.

As you probably know the residual pressure valve keeps a slight pressure on the wheel cylinders to prevent fluid leakage past the wheel cylinder cups when the circuit is not energized, compromised brake return hardware and cylinder corrosion are the usual suspects for dragging brakes.

[rockrat]

Thanks for the thoughts. Never thought about the rusty steel closing up the rubber hoses. I'll need to check for that and the rest of the list tomorrow.

Thanks again.
rock~

[Willy]

It wouldn't be so much the rusty steel as the rubber flex lines.

What can happen is the the inner liner partially separates from the hose and acts as a one way flapper valve causing a restriction in fluid return.

[dhammer]

Another thing to check is the parking brake cables. If the cables are rusted the parking brake might be partially activated all of the time.

[knedvecki]

Did you check the wear pattern on the brake linings? Could tell more of a story.